Sublimator having integrally formed closure bars on a porous plate

ABSTRACT

A sublimator includes a porous plate having a first surface comprising a low pressure side and a second surface comprising a high pressure side that allows a sublimate to move through the porous plate from the high pressure side to the low pressure side, and wherein the second surface defines a primary heat transfer surface. The sublimator also includes: a plurality of secondary heat transfer surfaces integrally formed on the primary heat transfer surface to facilitate flow and evenly distribute the sublimate across the high pressure side of the porous plate; and one or more closure bars formed integrally formed along an outer end of the plate and formed by an advanced manufacturing technique.

BACKGROUND

Exemplary embodiments pertain to the art of sublimator heat exchangers and, in particular, to a sublimator heat exchanger having structural members formed by an advance manufacturing technique.

A sublimator takes a fluid to be cooled and transfers the heat contained therein to a sublimate that is sublimated. A sublimator typically includes a metallic porous plate that is exposed to space vacuum on one side. It is supplied with a sublimate such as expendable feed-water on the other side. In operation, the feed-water freezes on the porous plate surface, and the vacuum side progressively sublimes water from this ice to the vacuum of space as waste heat is introduced into the plate.

Traditionally, the porous plate through which the sublimate sublimates includes plurality of fins that are individually attached to the porous plate. Depending upon the application, there can be several thousand fins that are attached to the porous plate with each fin segment being, incrementally spot welded to the porous plate in many locations. Further, the porous plate will include One, or more closure bars disposed on outer sides of the fins. The closure bars provide support to additional portions of the sublimator and may serve to define an outer boundary for the sublimate. The closure bars are also spot welded on the porous plate.

The spot welding is labor intensive and time consuming. Further, maintaining weld quality through this process requires constant tool maintenance and frequent quality inspections which increases overall manufactory cost.

BRIEF DESCRIPTION

Disclosed is a sublimator that includes: a porous plate having a first surface comprising a low pressure side and a second surface comprising a high pressure side such that a sublimate is configured to move through the porous plate from the high pressure side to the low pressure side, and wherein the second surface defines a primary heat transfer surface; a plurality of secondary heat transfer surfaces integrally formed on the primary heat transfer surface to facilitate flow and evenly distribute sublimate across the high pressure side of the porous plate; and one or more closure bars formed integrally formed along an outer end of the plate and formed by an advanced manufacturing technique.

In another embodiment, a sublimator is disclosed that includes: a sublimate chamber having a first side and a second side; a fluid chamber positioned on the first side of the sublimate chamber, wherein the fluid chamber is configured to receive a fluid to be cooled; and a porous plate having a first surface comprising a low pressure side and a second surface comprising a high pressure side. The high pressure side is positioned on the second side of the sublimate chamber such that sublimate is configured to move through the porous plate from the high pressure side to the low pressure side, the second surface of the porous plate defines a primary heat transfer surface, the porous plate includes a plurality of secondary heat transfer surfaces integrally formed on the primary heat transfer surface to facilitate flow and evenly distribute sublimate across the high pressure side of the porous plate, and the porous plate includes one or more closure bars formed integrally formed along an outer end of the plate and formed by an advanced manufacturing technique

In any embodiment of a sublimator previously disclosed, the advanced manufacturing technique is one of: laser-sintering, stereolithography, and fused deposition.

In any embodiment of a sublimator previously disclosed, the plurality of secondary heat transfer surfaces comprise a plurality fins extending outwardly from the primary heat transfer surface.

In any embodiment of a sublimator previously disclosed, the sublimator further includes: an intermediate plate having a first side and a second side facing opposite the first side, wherein the first side is spaced apart from the high pressure side of the porous plate and contacts the one or more closure bars to define a sublimate chamber, and wherein the second side at least partially encloses a fluid chamber configured to cool a fluid within the fluid chamber.

In any embodiment of a sublimator previously disclosed, the sublimator further includes an inlet to direct the sublimate into the sublimate chamber to flow across the primary and secondary heat transfer surfaces.

In any embodiment of a sublimator previously disclosed, the sublimator further includes a sublimate supply in fluid communication with the inlet to replenish sublimate that sublimates from the low pressure side of the porous plate into an external environment.

In any embodiment of a sublimator previously disclosed, the plurality of secondary heat transfer surfaces comprise a plurality of fins placed in a predetermined arrangement to optimize heat sink with heat flux input.

In any embodiment of a sublimator previously disclosed, a height of the plurality of secondary heat transfer surfaces is the same as a height of the one or more closure bars.

In any embodiment of a sublimator previously disclosed, the plurality of secondary heat transfer surfaces comprise a plurality of fins placed in a predetermined arrangement to optimize heat sink with heat flux input.

In any embodiment of a sublimator previously disclosed, a height of the plurality of secondary heat transfer surfaces is the same as a height of the one or more closure bars.

In one embodiment a method of making a sublimator is disclosed. The method includes: providing a porous plate having a first surface comprising a low pressure side and a second surface comprising a high pressure side such that sublimate is configured to move through the porous plate from the high pressure side to the low pressure side, and wherein the second surface defines a primary heat transfer surface; and integrally forming at least one closure bars on the porous plate by using an additive manufacturing.

In one embodiment, any method previously disclosed further includes integrally forming with an additive manufacturing process a plurality of secondary heat transfer surfaces on the primary heat transfer surface to facilitate flow and evenly distribute sublimate across the high pressure side of the porous plate.

In one embodiment, in any method previously disclosed the additive manufacturing process is one of: laser-sintering, stereolithography, and fused deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 shows a schematic representation of a sublimator according to one embodiment;

FIG. 2A is an exploded view of a conventional porous plate that includes welded fins and closure bars;

FIG. 2B shows a portion of a completed version of the porous plate of FIG. 2A; and

FIG. 3 shows a portion of a porous plate according to one embodiment.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

FIG. 1 shows a sublimator 10 that includes a sublimate chamber 12 having a first side 14 and a second side 16. A fluid chamber 18 is positioned on the first side 14 of the sublimate chamber 12. The fluid chamber 18 is configured to receive a fluid 20 to be cooled. A porous plate 22 has a first surface 24 comprising a low pressure side Lp and a second surface 26 comprising a high pressure side Hp. The high pressure side Hp is positioned on the second side 16 of the sublimate chamber 12 such that sublimate 28 is configured to move through the porous plate 22 from the high pressure side Hp to the low pressure side Lp. The second surface 26 of the porous plate 22 defines a primary heat transfer surface. The porous plate 22 also includes a plurality of secondary heat transfer surfaces 30 (or fins) formed on the primary heat transfer surface to facilitate flow and evenly distribute sublimate across the high pressure side Hp of the porous plate 22. As disclosed more fully below, the porous plate 22 also includes closure bars 52 formed on one or-more outer sides of the porous plate 22. The closure bars 52 and the fins 30 are shown as being formed of the same material but that is not required. Also, the height of the closure bars 52 and the fins 30 can be different from one another.

The fluid chamber 18 comprises an area that is enclosed by a housing 32 that includes an intermediate plate portion 34 that is located between the sublimate chamber 12 and the fluid chamber 18. While a single fluid chamber 18 and a single sublimate chamber are shown, it should be understood that there could be additional fluid chambers 18 and additional sublimate chambers 12. This will be discussed in greater detail below.

In one embodiment, the closure bars 52 contact the intermediate plate 34 and define outer boundaries of the sublimate chamber 12.

The sublimator 10 includes an inlet 40 to direct the sublimate 28 into the sublimate chamber 12 to flow across the primary and secondary heat transfer surfaces. A sublimate supply 42 is in fluid communication with the inlet 40 to replenish sublimate that sublimates from the low pressure side Lp of the porous plate 22 into an external environment E, such as outer space for example. A header 44 fluidly connects the inlet 40 to the sublimate chamber 12.

The sublimator 10 is used with a sublimate 28 that has a triple point where equilibrium of vapor, liquid, and solid will occur at a predetermined temperature or pressure and there is available an environment at or below this condition in one example, the sublimate 28 comprises water: however, other types of sublimate could also be used. The sublimate 28 is directed into the sublimate chamber 12 from the pressurized supply 42. The sublimate 28 then passes through the porous material that forms the porous plate 22 and freezes when exposed to the low pressure side Lp to form a layer of ice 50 that blocks further sublimate 28 from exiting the low pressure side Lp of the porous plate 22.

The sublimate 28 sublimates into the external environment E as heat is conducted to the porous plate 22 due to the heat exchange between the fluid 20 to be cooled and the sublimate 28 in the sublimate chamber 12. As the sublimate 28 sublimates away from the porous plate 22 and the solid sublimate becomes depleted, more sublimate is automatically used to replenish the porous plate 22.

In one example, the porous plate 22 is comprised of a stainless steel material having a pore size of approximately 0.5 microns. Other types of porous materials could also be used: however, the material needs to have a porous characteristic that facilitates formation of the necessary layer of ice 50 for sublimation. Each pore essentially becomes plugged with ice that has a surface exposed to the outer space environment E. As sublimation occurs at this surface, the thickness of the layer of ice 50 is reduced until it can no longer support the internal pressure within the chamber 12 and the sublimate will begin to pass into the external environment E. When the sublimate is exposed to this lower pressure level below its triple point, the sublimate freezes and reforms the ice.

In the example shown, the entire high pressure side Hp of the porous plate 22 is overlaid on the sublimate chamber 12 to provide maximum exposure. The fins 30 formed on the porous plate further enhance flow and improve distribution across and through the porous plate 22. This allows the formation of a uniform sheet of ice 50 across the low pressure side Lp of the porous plate 22. The fluid 20 that is to be cooled transmits heat through the intermediate plate portion 34 and through the sublimate 28 and eventually into the porous plate 22. The heat sublimates the ice at a rate that is directly proportional to the heat load and the fluid 20 to be cooled is discharged at a temperature that is lower than when the fluid entered the fluid chamber 18.

As discussed above, while only a single fluid chamber or passage 18 is shown in FIG. 1, the sublimator 10 can include multiple fluid passages in parallel. Adjacent to each fluid passage 18 is a sublimate passage or chamber 12, which are fed by a common inlet header 44. The sublimate flows in via the header 44 and exits the sublimator either by sublimation or evaporation depending on the “sink” temperature. The “sink” is the porous plate 22, and as the range of heat flux into the porous plate 22 varies, the heat rejection capability of the sublimator moves coincidently. This relationship drives the demand for efficient integral construction of the sublimate passage or chamber 12 with respect to the primary (porous plate surface) and secondary (protrusions/fins) heat transfer surfaces. Proper layout of the secondary heat transfer surfaces is essential to balancing the heat flux to heat sink temperature relationship. Maintaining a tight control band on the sink capacity will produce a fleet of sublimators with minimal unit to unit variability in heat rejection capability.

With reference now to FIGS. 2A and 2B, prior art fins 100 are formed as part of a fin plate 102 that is spot welded to the porous plate 22. Spot welding is a manufacturing method which leads to variability in the overall heat transfer effectiveness of a sublimator due to its inherent quality instability. The variability of quality in the small spot welds effects the ability of heat to transfer from the fluid to be cooled to the sublimate within the porous plate. This poor connection equates to a larger device for a given heat load. The porous plate also has closure bars 104 that are brazed to the porous plate 22. The process of both spot welding and brazing are labor intensive, time consuming and requires constant tool maintenance to stay within the required quality tolerance.

With reference now to FIG. 3, as disclosed herein, the porous plate 22 has one or more of the closure bar 204 and the fins 30 formed by directly thereon by an advanced manufacturing technique. Such advanced manufacturing, techniques can include, for example, additive manufacturing. In that regard, a variety of additive manufacturing methods can be used to produce the integrally formed fins 30 and closure bar 204. The process is used to form or grow these elements directly on the porous plate 22. Processes such as laser-sintering, stereolithography, and fused deposition modeling are just some of the example processes that could be used to integrally form the elements the porous plate. The shape, size, location and density of the elements can be varied as needed to produce the optimum heat sink characteristics to precisely match the heat flux input.

The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.

While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims. 

What is claimed is:
 1. A sublimator comprising: a porous plate having a first surface comprising a low pressure side and a second surface comprising a high pressure side that allows a sublimate to move through the porous plate from the high pressure side to the low pressure side, and wherein the second surface defines a primary heat transfer surface; a plurality of secondary heat transfer surfaces integrally formed on the primary heat transfer surface to facilitate flow and evenly distribute the sublimate across the high pressure side of the porous plate; and one or more closure bars formed integrally formed along an outer end of the plate and formed by an advanced manufacturing technique.
 2. The sublimator of claim 1, wherein the advanced manufacturing technique is one of: laser-sintering, stereolithography, and fused deposition.
 3. The sublimator according to claim 1, wherein the plurality of secondary heat transfer surfaces comprise a plurality fins extending outwardly from the primary heat transfer surface.
 4. The sublimator according to claim 3, further comprising: an intermediate plate having a first side and a second side facing opposite the first side, wherein the first side is spaced apart from the high pressure side of the porous plate and contacts the one or more closure bars to define a sublimate chamber, and wherein the second side at least partially encloses a fluid chamber configured to cool a fluid within the fluid chamber.
 5. The sublimator according to claim 4, further including an inlet to direct sublimate into the sublimate chamber to flow across the primary and secondary heat transfer surfaces.
 6. The sublimator according to claim 4, further including a sublimate supply in fluid communication with the inlet to replenish sublimate that sublimates from the low pressure side of the porous plate into an external environment.
 7. The sublimator according to claim 1, wherein the plurality of secondary heat transfer surfaces comprise a plurality of fins placed in a predetermined arrangement to optimize heat sink with heat flux input.
 8. The sublimator according to claim 1, wherein a height of the plurality of secondary heat transfer surfaces is the same as a height of the one or more closure bars.
 9. A sublimator comprising: a sublimate chamber having a first side and a second side; a fluid chamber positioned on the first side of the sublimate chamber, wherein the fluid chamber is configured to receive a fluid to be cooled; and a porous plate having a first surface comprising a low pressure side and a second surface comprising a high pressure side, wherein the high pressure side is positioned on the second side of the sublimate chamber such that sublimate can move through the porous plate from the high pressure side to the low pressure side, and wherein the second surface of the porous plate defines a primary heat transfer surface, and wherein the porous plate includes a plurality of secondary heat transfer surfaces integrally thrilled on the primary heat transfer surface to facilitate flow and evenly distribute the sublimate across the high pressure side of the porous plate, and wherein the porous plate includes one or more closure bars formed integrally formed along an outer end of the plate and formed by an advanced manufacturing technique.
 10. The sublimator according to claim 9, wherein the advanced manufacturing technique is one of: laser-sintering, stereolithography, and fused deposition.
 11. The sublimator according to claim 9, wherein the plurality of secondary heat transfer surfaces comprise a plurality fins extending outwardly from the primary heat transfer surface.
 12. The sublimator according to claim 9, wherein the plurality of secondary heat transfer surfaces comprise a plurality of fins placed in a predetermined arrangement to optimize heat sink with heat flux input.
 13. The sublimator according to claim 9, wherein a height of the plurality of secondary heat transfer surfaces is the same as a height of the one or more closure bars.
 14. A method of making a sublimator comprising the steps of: providing a porous plate having a first surface comprising a low pressure side and a second surface comprising a high pressure side such that sublimate is configured to move through the porous plate from the high pressure side to the low pressure side, and wherein the second surface defines a primary heat transfer surface; and integrally forming at least one closure bars on the porous plate by using an additive manufacturing.
 15. The method of claim 14, further comprising: integrally forming with an additive manufacturing process a plurality of secondary heat transfer surfaces on the primary heat transfer surface to facilitate flow and evenly distribute sublimate across the high pressure side of the porous plate.
 16. The method of claim 14, wherein the additive manufacturing process is one of: laser-sintering, stereolithography, and fused deposition. 